Electrolyte bath composition for the electrolytic production of lusterless and of corrosion resistant surfaces on metals



United States Patent 3,366,558 ELECTROLY'IE BATH COMPQSTTION FOR THE ELECTROLY'HC PRODUCTION OF LUSTER- LESS AND 01* CORRGSIGN RESHSTANT SUR- FACES ON METALS Akio Shiga and Edeyuki Furukawa, Machida-shi, Japan,

assignors to Kyowa Hakko Kogyo 'Co., Ltd, Chiyodakn, Tokyo, Japan, a corporation of Japan No Drawing. Filed Feb. 24, 165, Ser. N 0. 435,051 Claims priority, application Japan, Feb. 27, 1964, 39/ 10,380- 11 Claims. (Cl. 204-1405) The present invention relates to an improvement in the production of a matted or lusterless corrosion resistant surface on metal by an electrolytic polishing method.

Methods of roughening the surface of corrosion resistant and other metals are known, but only purely chemical or physical methods are now being put to practical use, thus, the current methods involve treatment with strong acid (chemical) or with sand-blast or steam-blast (physical). These methods do not result in a corrosionproof film on the surface of the treated metal, an improvement in this respect has thus been a long-standing desideratum in this art.

The primary purpose of this invention is to satisfy or fulfill such desideratum.

This is accomplished according to the present process, according to which the defects of the conventional procedures are obviated and a perfect corrosion-proof lusterless surface is produced on the metal being electrolytically polished, by employing a socalled electrolytic polishing solution which contains inter alia aminoacetic acid (glycine) or a salt thereof and/or Z-aminopropionic acid (5- alanine) or a salt thereof and/or gluconic acid or a salt thereof, as essential additaments. The presence of nicotinic acid or a salt thereof and/or nicotinamide in the electrolyte bath tends to enhance the sought-for results, but the use of these further additaments is not indispensible.

Apart from the production of the corrosion-resistant lusterless surface on the metal being treated, an electrolytic polishing solution composed according to the present invention is endowed with stability which enables it to be employed for a long period of time without deteriorative ageing and without change in the composition of the solution. Moreover, the new electrolytic polishing method involves a saving of time and labor, in comparison to prior known processes.

No prejudical effects on personnel carrying out the polishing, such as is frequently an incident of physical processes of e.g. the blasting type, are here involved.

The procedure according to this invention is also advantageous in that an electrolyte bath of a composition according to the invention enables the electrolytic polishing to be carried out at ambient temperature, e.g. at 15 to 30 C., and at a lower voltage and amperage than the working voltage and amperage required for the conventional electrolyte solution. Thus, a voltage of about 5 volts and an amperage of about 20 arnperes/dm. suflice for carrying out the electrolytic polishing of the present invention.

The electrolytic polishing per se does not constitute the precise point of novelty of the present invention, except as it is carried out with the use of an electrolyte bath composed as herein disclosed. The precise point of novelty thus resides in the use of the previously enumerated additarnents.

Thus, the details of the electrolytic polishing procedure are variable without departing from the spirit and scope of this invention, it use is made of the novel electrolyte bath composition. Moreover, the composition of the bath is itself variable, apart from the additaments above set forth, thus, except for the latter, such composition may be more or less conventional. Accordingly, in addition to the indispensible and/ or optional additaments of this invention, the electrolyte bath will, as is conventional, contain an acid, preferably sulfuric acid, with which there may be admixed another acid, e.g. phosphoric acid.

Thus, the novel compositions according to this invention, may correspond to the following, per 200 milliliters of water:

Grams Mineral acid 50 to 180 Aminoalkanoic acid compound 5 to 40 and/or Gluconic acid compound 2 to 30 Nicotinic acid compound 0120 30 The mineral acid is sulfuric acid or phosphoric acid or a mixture thereof, in the latter event, the mixture preferably contains at least 30 grams of sulfuric acid per 200 milliliters of water. The acids may e.g. be used in the form of the orthophosphoric acid and the 92% concentrated sulfuric acid. The aminoalkanoic acid compound is either glycine, alkali metal glycinate, fi-alanine or alkali metal 2-aminopropionate or a mixture thereof. The gluconic acid compound is either gluconic acid or alkali metal gluconate. The nicotinic acid compound is either nicotinic acid or alkali metal nicotinate or nicotinamide. The sum gluconic acid compound-I-nicotinic acid compound preferably does not exceed 30 grams per 200 milliliters of water-in thebath.

The polishing process according to this invention is very expeditiously carried out, and there is obtained on the metal being treated a surface which is uniformly corrosion-proof and of a uniform lusterless ground (sometimes referred to as pear-like) surface aspect. The treatment period usually is completed within from a minute and a half to about 3 minutes. Use is conveniently made of a lead or carbon, i.e. insoluble, cathode, while the metal being polished constitutes the cathode. The term polishing is here used in its special sense since actually no brightening or imparting of a luster is achieved; in fact, as hereinbefore emphasized, it is an object of the invention to produce a matted or lusterless surface on the metal being polished.

An outstanding feature of the invention is that it produces the objective corrosion-proof and lusterless ground surface even on materials such as 188 stainless steel, 18-, 16- or l3-chrome steel and the like. Similar results are obtainable on other metals, e.g. ferrous metals such as cast iron and the like, aluminum, aluminum alloys as duralumin, etc.

Typical exemplary and presently preferred embodiments of the present invention are as follows:

Example 1 The electrolytic polishing was carried out at room temperature (about 25 C.) using 18-8 stainless steel as anode and lead as cathode in an electrolyte solution of the following composition and under the following electrolytic conditions:

Sulfuric acid grams 9O Glycine do 10 Sodium gluconate do 5 Water milliliters 200 Voltage volts 5 Amperage amperes/dm. 20

The steel being polished was covered by a surface film of good corrosion resistance and without luster in about 3 minutes.

Example 2 The polishing treatment was carried out at 30 C. using a carbon cathode and an l8-chrome steel anode in an electrolyte solution of the following composition:

Sulfuric acid "grams" 90 fl-alanine do 10 Sodium gluconate do Water "milliliters" 200 Voltage volts 5 Amperage "amperes/din?" 20 The steel being polished was provided in a minute and and a half with a surface of good corrosion resistance without luster. 1

Example 3 The electrolytic polishing was carried out at 30 C. using carbon as cathode and l8-chrome steel as anode in an electrolyte solution of the following composition:

Sulfuric acid grams 90 fi-alanine do Nicotinic acid amide do 5 Water milliliters 200 Voltage volts 5 Amperage amperes/ dm. 20

The 18-chrome steel was polished in a minute and a half with a surface of good corrosion resistance and without luster.

Example 4 The electrolysis was carried out, using l88 stainless steel as anode and carbon as cathode in an electrolyte solution of the following composition:

Sulfuric acid grams 90 Phosphoric acid do 85 Glycine do 10 Sodium gluconate do 5 Water milliliters 200 The voltage was 3.5 volts and the amperage was 12 amperes/dmfi. The 18-8 stainless steel used was polished without luster.

Example 5 The electrolysis was carried out, using lS-chrome steel as anode and carbon as cathode in an electrolyte solution of the following composition:

Sulfuric acid grams 90 Phosphoric acid do 85 Ethylene glycol milliliters 2O Glycine "grams" 10 Sodium gluconate do 5 Water milliliters 200 of an additive selected from the group consisting of glycine, alkali metal salts of glycine, B-alanine, alkali metal salts of lit-alanine and mixtures thereof, with said metal constituting the anode and with a cathode which is insoluble in said solution. 7

2. The method of claim 1, wherein said solution also contains a member selected from the group consisting of nicotinic acid, alkali metal nicotinates and nicotinamide.

3. The method of claim 1, wherein said metal is stainless steel.

4. The method of claim 1, wherein said solution contains from 50 to grams of mineral acid and from 5 to 40 grams of said additive, per 200 milliliters of water.

5. The method of claim 4, wherein said solution also contains up to 30 grams of a member selected from the group consisting of nicotinic acid, alkali metal nicotinates and nicotinamide.

6. The method of claim 1, wherein the electrolyzing is carried out at a voltage of from 5 to 40 volts and at a current density of from 12 to 20 amperes per square decimeter.

7. A method for electrolytically treating a metal selected from the group consisting of aluminum, alloys of aluminum, iron and alloys of iron to provide a corrosion-resistant matted surface thereon which comprises electrolyzing an aqueous solution containing, per 200 milliliters of water, from St to 180 grams of sulfuric acid and from 5 to 40 grams of an additive selected from the group consisting of glycine, alkali metal salts of glycine, fl-alanine, alkalimetal salts of ,B-alanine and mixtures thereof, with said metal constituting the anode and with a cathode which is insoluble in said solution, at a voltage of from 5 to 40 volts and at a current density of from 12 to 20 amperes per square decimeter.

8. The method of claim 7, wherein said solution also contains up to 30 grams of a member selected from the group consisting of nicotinic acid, alkali metal nicotinates and nicotinamide.

9. The process of claim 8, wherein said solution contains phosphoric acid and at least 30 grams of sulfuric acid, the total amount of these acids ranging from 50 to 180 grams per ZOOmilliliters of water.

10. An electrolyte bath composition comprising an aqueous solution containing, per 200 milliliters of water, about 50 grams to about 180 grams of a mineral acid selected from the group consisting of sulfuric acid, phosphoric acid and mixtures thereof and (A) from about 5 to about 40 grams of an additive selected from the group consisting of glycine, alkali metal salts of glycine, fialanine, alkali metal salts of B-alanine and mixtures thereof and (B) and up to 30 grams of an additive selected from the group consisting of nicotinic acid, alkali metal nicotinates and nicotinamide.

11. The electrolyte bath composition of claim 10, wherein said solution contains phosphoric acid and at least 30 grams of sulfuric acid, the total amount of these acids ranging from 50 to 180 grams per 200 milliliters of water.

References Cited UNITED STATES PATENTS 2,694,001 11/1954 Hayes et al. 25279.4

ROBERT K. MIHALEK, Primary Examiner. 

1. A METHOD FOR ELECTROLYTICALLY POLISHING A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ALLOYS OF ALUMINUM, IRON AND ALLOYS OF IRON TO PROVIDE A CORROSIONRESISTANT MATTED SURFACE THEREON WHICH COMPRISES ELECTROLYZING AN AQUEOUS SOLUTION CONTAINING A MINERAL ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID, PHOSPHORIC ACID AND MIXTURES THEREOF AND AN EFFECTIVE AMOUNT OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF GLYCINE, ALKALI METAL SALTS OF GLYCINE, B-ALANINE, ALKALI METAL SALTS OF B-ALANINE AND MIXTURES THEREOF, WITH SAID METAL CONSTITUTING THE ANODE AND WITH A CATHODE WHICH IS INSOLUBLE IN SAID SOLUTION.
 10. AN ELECTROLYTE BATH COMPOSITION COMPRISING AN AQUEOUS SOLUTION CONTAINING, PER 200 MILLILITERS OF WATER, ABOUT 50 GRAMS TO ABOUT 180 GRAMS OF A MINERAL ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID, PHOSPHORIC ACID AND MIXTURES THEREOF AND (A) FROM ABOUT 5 TO ABOUT 40 GRAMS OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF GLYCINE, ALKALI METAL SALTS OF GLYCINE, BALANINE, ALKALI METAL SALTS OF B-ALANINE AND MIXTURES THEREOF AN (B) AND UP TO 30 GRAMS OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF NICOTINIC ACID, ALKALI METAL NICOTINATES AND NICOTINAMIDE. 